Efficient Asymmetric Synthesis of 2,6-Disubstituted 2H-Dihydropyrans via a Catalytic Hetero-Diels-Alder/Allylboration Sequence

Article abstract of DOI:10.1002/adsc.200303127

[4 + 2] Cycloaddition of (E)-3-borylacrolein 1 with ethyl vinyl ether, catalysed by chromium complex (1R,25) or (15,2R) 2, led to the corresponding cycloadducts with high diastereo- and enantioselectivities. Further reaction with aldehydes offers an attractive asymmetric route to synthetically useful substituted 3,4-dihydro-2H-pyrans.